@Mohamad Guene Regarding your question, it really depends on the investor.

As I'd imagined, it seems like there are no hard-and-fast ways that a deal must be structured, but rather there is room for flexibility depending on the situation, and in any case consultation with experienced professionals at every level is key.

depending on where you are in NJ you might have the Lehigh Valley in PA a couple hours away, or Delaware, etc. you can go to meetups, see places in person, and start to build a network.

It really depends how motivated you are.

Depends what you're looking for really, it might be worth discussing your strategies and goals with a broker, a national lender, and a local CU. 

How much profit you make depends largely on your targeted clientele and your property management. 

Ratios like 0.7% or 0.8% can still work, but it depends on your market and expenses.

I find that depending on the market $300-500/mo are fairly normal and if compared to what you would pay with a single family home on some utilities, maintenance, and management, it's a good deal.

Interesting approach, how would multiple refi affect my credit score?

It all really depends on your appetite for risk.